Superconducting thin film having columnar pinning centers utilizing nano dots and method of making the same

ABSTRACT

A superconducting thin film is disclosed having columnar pinning centers utilizing nano dots, and comprising nano dots ( 3 ) which are formed insularly on a substrate ( 2 ) and three-dimensionally in shape and composed of a material other than a superconducting material and also other than a material of which the substrate is formed, columnar defects ( 4 ) composed of the superconducting material and grown on the nano dots ( 3 ), respectively, a lattice defect ( 6 ) formed on a said columnar defect ( 4 ), and a thin film of the superconducting material ( 5 ) formed in those areas on the substrate which are other than those where said columnar defects are formed. The superconducting thin film ( 5 ) is prepared by depositing the material other than the superconducting material on the substrate ( 2 ) while controlling the substrate ( 2 ) temperature, and the film thickness of the material deposited so to coagulate the deposited material to form the nano dots ( 3 ), and then growing a thin film of the superconducting material ( 5 ) on the substrate ( 2 ). An improved superconducting thin film is thus provided which regardless of its type is at least ten times higher in critical current density than an exiting superconducting thin film, and which can also be manufactured at a low cost. And, being large in critical superconducting current density and critical superconducting magnetic field, it is advantageously applicable to the technical fields of cryogenic electronics and microwaves.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of Ser. No. 10/480,942, filed May 12,2004, which is a National Stage Application Under 35 U.S.C. § 371 ofPCT/JP02/06007, filed Jun. 17, 2002, which is based upon and claims thebenefit of priority from the prior Japanese Patent Application No.2001-185597, filed Jun. 19, 2001, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a superconducting thin film that islarge in critical superconducting current density and criticalsuperconducting magnetic field, which is advantageously applicable tothe technical fields of cryogenic electronics and microwaves. Theinvention also relates to a method of making such a superconducting thinfilm.

BACKGROUND ART

In the past, columnar or extended pinning centers could be created in asuperconducting thin film only through irradiation with a high energybeam of neutrons or heavy ions (see L. Civale et al., Physical ReviewLetters 67 No. 5, 648, 1991). According to this method, a materialdamaged by irradiation with a high energy beam of neutrons or heavy ionsis arrayed regularly to form extremely effective columnar pinningcenters, namely columnar or extended defects which enhance its criticalcurrent density and critical magnetic field. Theoretically, it has beenproven by A. Buzdin and M. Daumens (see Physica C, 294, 297, 1998) thata highest pinning effect is achieved if the columnar defect iscross-sectionally in the form of an elongate ellipse, namely if it is inthe form of a thin stripe. In order to form such a columnar or extendeddefect, it is necessary to irradiate a substrate with a heavy ion beamat an angle lower than 90 degrees to its surface.

It has now been known that pinning centers can also be formed in asuperconducting thin film by photolithography and lift-off techniques tocreate a regular array of dots or holes (see M. Baert et al., PhysicalReview Letters, 74, 3269, 1995).

The abovementioned method of driving a high energy beam of neutrons orheavy ions into is recognized to be extremely useful in making asuperconducting thin film with high critical current density, but itrequires an accelerator for high energy particles and thus has theproblem that its practice is very costly.

Columnar defects having a striped cross section and formed byirradiating a substrate with heavy ions at a low angle have their axesinclined to the c-axis of a superconducting thin film and also deviatedfrom a direction in which a magnetic field is applied generally. Then,for defects to be pinned, it is necessary to tilt the direction ofmagnetic flux, which causes the pinning free energy to be decreased,however. This is the reason why defects of this type are only effectivein a small magnetic field.

On the other hand, a regular array of dots or holes formed by utilizingphotolithography or lift-off is not much effective for the reasons asfollows. First, their size is larger than 0.1 μm and their length islonger than the superconducting coherence length. Second, their surfacedensity is small and the distance between adjacent dots or holes is 1 μmor more. Under these conditions, it is only in a magnetic field as lowas 1 mT that the critical current density can be increased.

DISCLOSURE OF THE INVENTION

In view of the aforementioned problems in the prior art, the presentinvention has for its object to provide a method whereby asuperconducting thin film regardless of its type can be preparedexhibiting an increased critical current density that is at least tentimes higher than that which an existing superconducting thin film doesand further at a low cost.

In order to achieve the object mentioned above, there is provided inaccordance with the present invention a superconducting thin film havingcolumnar pinning centers utilizing nano dots, characterized in that itcomprises a substrate; nano dots or nano stripes which are formedinsularly on the substrate and three-dimensionally in shape and composedof a material other than a superconducting material and also other thana material of which the substrate is formed; columnar or extendeddefects composed of the said superconducting material which are grown onthe said nano dots or nano stripes respectively, possibly with a latticedefect; and a thin film of the said superconducting material formed inthose areas on the said substrate which are other than those where thesaid columnar defects are formed.

With the superconducting thin film so structured, the columnar orextended defects on the three-dimensionally shaped nano dots or nanostripes and possibly also the lattice defects on such nano dots orstripes serve as pinning centers to pin a magnetic flux and thereby tomake it immobile, thus leading to a sharp rise in the critical currentdensity and critical magnetic field which a superconducting thin filmexhibits.

In the abovementioned structure of the superconducting thin film, thesaid material other than a superconducting material and also other thana material of which the substrate is formed is preferably a metal, aninsulator, a semiconductor or a ferromagnetic material. With thesuperconducting thin film so constituted, the columnar defects which arenon-superconducting and formed on the three-dimensionally shaped nanodots or nano stripes act to pin the magnetic flux. If the material isferromagnetic, then there is added energy by the interaction of themagnetic flux and the magnetization of the ferromagnetic material, andthe magnetic flux is even more firmly pinned thereby.

In the aforementioned structure of the superconducting thin film,preferably the said nano dots which are three-dimensional in shape are20 nm or less in diameter and 6 nm or so in height and, being spacedapart from one another by an average distance of 50 nm or less areirregularly or randomly distributed on the said substrate. With thesuperconducting thin film so constructed, the effect of pinning themagnetic flux is augmented whereby both the critical current density andthe critical magnetic field are increased.

In the aforementioned structure of the superconducting thin film,preferably the said nano stripes which are three-dimensional in shapeare formed, each in the form of a stripe, along flanks of steps formedon the said substrate which is a substrate formed so that its facialorientation is inclined to its crystallographic axis. With thesuperconducting thin film so constructed, the columnar defect is formedon the nano stripe so that its cross section parallel to the substratesurface is a plane in the form of an elongate ellipse. As a result,there is the increased interaction energy between the magnetic flux andcolumnar defects, and the magnetic flux is even still more firmly pinnedthereby.

In the aforementioned structure of the superconducting thin film,specifically a said columnar defect is of an amorphous body composed ofsaid superconducting material, a non-superconductor, or a superconductorof low critical temperature, and it is formed columnarly perpendicularto a surface of the said substrate. According to this specific makeup,the columnar defects are non-superconducting to permit a magnetic fluxto enter, and act as pin centers to pin the magnetic flux.

Also, the said lattice defect may comprise a crystal dislocation of thesuperconducting material forming the said thin film. According to thismakeup, if the columnar defects are thinner in thickness than the thinfilm of the superconducting material, the pin centers are stillprovided, served by the crystal defects, e.g., dislocations, on thecolumnar defects.

In the aforementioned structure of the superconducting thin film, thesaid substrate may be a substrate of SrTiO₃, MgO or Al₂O₃, or asubstrate having a buffer layer of CeO₂ formed thereon; the saidmaterial other than the said superconducting material may be Ag, Mg orZn; and the said thin film may be a thin film composed of asuperconductor that can be expressed by composition formula:

(Cu_(1−x)Tl_(x))Ba_(1−y)Sr_(y)Ca₂Cu₃O_(z) where 0≦x≦1, 0≦y≦1, and 0<z.

Further, the said thin film may be a thin film composed of a selectivereduction type high temperature superconductor that is of a (Cu, M) hightemperature superconducting material which can be expressed by thefollowing composition formula:

Cu_(1−x)M_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

where M represents one or more metallic elements in an ionic formselected from the group that consists of Ti, Bi, Pb, Hg, In, Ga, Sn, Ti,V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os; and L represents one ormore elements selected from the group that consists of Mg and alkalimetal elements, and where 0≦x≦1.0, 0≦y≦1.0, 0≦z≦1, 0≦w≦4, and 1≦n≦16.

In these cases, it is possible to increase to about ten times higher thecritical current density which a superconducting thin film of aselective reduction type high temperature superconductor such as(Cu¹⁻¹Tl_(x))Ba_(1−y)Sr_(y)Ca₂Cu₃O_(z) orCu_(1−x)M_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)superconductor exhibits.

The present invention also provides a method of making a superconductingthin film having columnar pinning centers utilizing nano dots,characterized in that it comprises the steps of forming insularly on asubstrate, nano dots or nano stripes shaped three dimensionally andcomposed of a material other than a superconducting material and alsoother than a material of which the substrate is formed, and growing onthe said substrate a thin film composed of the said superconductingmaterial. According to this method makeup, a columnar defect of anamorphous or non-superconducting material is allowed to form on each ofnano dots or nano stripes distributed insularly on a substrate, possiblyalso with a crystal dislocation allowed to form on such a columnardefect whereby such a columnar defect or a dislocation becomes a pinningcenter in the superconducting thin film.

In the aforementioned method makeup, specifically the said nano dotsshaped three-dimensionally and composed of a material other than thesaid superconducting material are formed by depositing the said materialinsularly on the said substrate by a technique selected from the groupwhich consists of sputtering, vaporization, laser ablation, CVD and MBEwhile controlling the substrate temperature, the deposition rate of thesaid material and the film thickness of the said material deposited,thereby coagulating the deposited material on the said substrate to formthe said three-dimensionally shaped nano dots insularly thereon.According to this method makeup, nano dots can be formed which are 20 nmor less in diameter and 6 nm or less in height and, being spaced apartfrom one another by an average distance of 50 nm or less, areirregularly or randomly distributed on the substrate.

In the aforementioned method makeup, specifically the said nano stripesshaped three-dimensionally and composed of a material other than thesaid superconducting material are formed by forming a substrate so thatits facial orientation is inclined to its crystallographic axis, anddepositing the said material insularly on the said substrate by atechnique selected from the group which consists of sputtering,vaporization, laser ablation, CVD and MBE while controlling thesubstrate temperature, the deposition rate of the said material and thefilm thickness of the said material deposited, thereby permitting thedeposited material on the said substrate to selectively grow in regionsof steps formed thereon and thereby to form the said three-dimensionallyshaped nano stripes insularly on the said substrate. This method makesit possible to create the nano stripes which are formed along flanks ofthe steps and have the elongated elliptic cross section parallel to thesubstrate surface.

Also, the said thin film of the superconducting material is grown onsaid substrate specifically by crystal growth of the saidsuperconducting material, by way of a technique selected from the groupwhich consists of sputtering, vaporization, laser ablation, CVD and MBE,on the said substrate having the said nano dots or nano stripes formedthereon.

Alternatively, the said thin film of the superconducting material isgrown on said substrate specifically by crystal growth of the saidsuperconducting material, by way of amorphous phase epitaxial process,on the said substrate having the said nano dots or nano stripes formedthereon. This method makes it possible to create the superconductingthin films of (Cu,Tl)Ba₂SrCa₂Cu₃O_(y) having the pinning centers.

According to the present invention, a superconducting thin film isobtained which is high in both critical superconducting current densityand magnetic filed, and such a superconducting thin film can bemanufactured at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will better be understood from the followingdetailed description and the drawings attached hereto showing certainillustrative forms of implementation of the present invention. In thisconnection, it should be noted that such forms of implementationillustrated in the accompanying drawings hereof are intended in no wayto limit the present invention but to facilitate an explanation andunderstanding thereof. In the drawings:

FIG. 1 is a cross sectional view illustrating the structure of asuperconducting thin film having pinning centers formed from nano dotsin accordance with the present invention;

FIG. 2 is a transverse cross sectional view illustrating the arrangementof nano stripes according to the present invention;

FIG. 3 is a view illustrating an AFM image of Ag nano dots formed on aSrTiO₃ single crystal substrate; and

FIG. 4 is a graph illustrating, as results of measurement, thedependency of critical current density on magnetic filed for asuperconducting thin film having Ag nano dots and a superconducting thinfilm not provided with Ag nano dots.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail withreference to certain suitable forms of implementation thereofillustrated in the drawing figures.

At the outset, mention is made of a first form of implementation of thepresent invention. FIG. 1 is a cross sectional view illustrating thestructure of a superconducting thin film having pinning centers formedfrom nano dots in accordance with the present invention. In the Figure,a superconducting thin film 1 having pinning centers is here structuredto comprise a substrate 2, nano dots 3 formed on the substrate 2,columnar (or extended) defects 4 formed on the nano dots 3,respectively, and a thin film of superconductor 5 formed in those areason the substrate 2 other than where the columnar defects 4 are formed.Further, a dislocation 6 may also be formed as extending from a columnardefect 4.

The nano dots 3 are composed of a material other than those of which thesubstrate 2 and the superconducting thin film 5 and may be, for example,a metal, an insulator, a semiconductor or a ferromagnetic material. Thenano dots 3 are 20 nm (nanometers) or less in diameter and around 6 nmin height, and are irregularly or randomly distributed on the substrate2 as they are spaced apart from one another by a mean distance of 50 nmor less. Each columnar defect 4 is in the form of a column having itsbasal plane formed by a nano dot 3 and having its axis extendingperpendicular to the surface of the substrate 2. The columnar defect 4is an amorphous body composed of a superconducting material; anon-superconductor; or a low critical temperature superconductor. Thelattice defect 6 is a crystal dislocation of the superconductingmaterial forming the thin film.

According to this makeup, an applied magnetic flux enters the columnardefect 4 on the nano dot 3 because of the columnar defect 4 being anon-superconductor and is pinned. Even if the columnar defect 4 does notreach the surface of the thin film of superconductor 5, the magneticflux is pinned by the crystal dislocations 6 each extending from the topof a columnar defect 4. If the nano dots are of a ferromagneticmaterial, there is the added interaction energy between the magneticflux and the magnetization of the ferromagnetic material, and hence themagnetic flux is even more firmly pinned thereby.

Since the columnar defects 4 each formed on a nano dot 3 are each of acolumnar shape of nano size reflecting the columnar shape of a nano dot3 having its axis perpendicular to the substrate surface and, beingspaced apart from one another by a distance or 50 nm or less, aredistributed irregularly or randomly over the substrate 2, their magneticflux pinning effect is large and the superconductivity of the thin filmis thus not broken even by its high superconducting current densityunder an increased magnetic field.

Mention is next made of a second form of implementation of the presentinvention.

FIG. 2 is a transverse cross sectional view illustrating the makeup ofnano stripes of a superconducting thin film having pinning centersaccording to the present invention. The Figure shows the shape anddistribution of nano stripes 8 formed on surfaces 7 of steps. The nanostripes 8 are each in the form of a thin stripe of nanometer size formedalong a flank 9 of a step and, being spaced apart from one another by adistance of 50 nm or less, are irregularly or randomly distributed.

As in the form of implementation shown in FIG. 1 for the nano dots, thenano stripes 8 are composed of a material other than those of which thesubstrate 2 and a thin film of superconductor 5 are composed, whichmaterial may be a metal, an insulator, a semiconductor or aferromagnetic material. A columnar defect is formed on each of the nanostripes 8, and the thin film of superconductor is formed in those areason the substrate other than where the columnar defects are formed.

According to this makeup, since columnar defects are formed each havinga shape in cross section that is an elongate ellipse or being a thinstripe, the magnetic flux pinning effect is further enhanced.

Mention is next made of a method of making a superconducting thin filmhaving pinning centers in accordance with the present invention.

Mention is first made of a method of making a superconducting thin filmhaving pinning centers formed from nano dots.

The method of making a superconducting thin film having pinning centersformed from nano dots comprises depositing a material other thansuperconductors on a substrate by using sputtering, evaporation, laserablation, CVD (chemical vapor deposition), or MBE (molecular beamepitaxy) while controlling the substrate temperature, the depositionrate of the material and the film thickness of the material deposited,thereby coagulating the deposited material on the substrate to formthree-dimensional nano dots insularly thereon. This process allows thenano dots having a diameter of 20 nm or less and a height of 6 nm or soand spaced apart by an average distance of 50 nm or less to be easilyformed as they are irregularly or randomly distributed on the substrate.

Next, a superconducting material is grown by crystal growth of thesuperconducting material on the substrate having the nano dots formedthereon by way of sputtering, vaporization, laser ablation, CVD, MBE orthe like technique. This process allows the superconducting materialgrown on the nano dots to form amorphous or non-superconducting columnardefects and the superconducting material to be grown on those areas onthe substrate other than where the nano dots have been formed to form athin film of superconductor. Alternatively, an amorphous epitaxialprocess as described in JP Patent No. 2,923,530 may be used to form sucha thin film of superconductor.

According to this method, a superconducting thin film can be obtainedhaving pinning centers formed from nano dots in accordance with thepresent invention.

Mention is next made of a method of forming a superconducting thin filmhaving pinning centers formed from nano stripes.

The method of forming a superconducting thin film having pinning centersformed from nano stripes makes use of a crystallographically inclinedsubstrate that is formed so that its facial orientation is inclined toits crystallographic axis. The angle of inclination may range betweenseveral and 10 degrees. Cutting out with such an inclination allowsincremental steps each in the order of a molecular layer to be formed onthe inclined substrate surface. Alternatively, such the substrate havingincremental steps in the order of a molecular layer may be formed byheat-treating a substrate cut out with an inclination under suitableconditions.

Then, a material other than superconductors is deposited on a substratehaving steps so formed, by sputtering, vaporization, laser ablation, CVDor MBE while controlling the substrate temperature, the deposition rateof the material and the film thickness of the material deposited, toform nano stripes, each in the form of a stripe of nano size, in regionsof flanks of the steps along the flanks.

Next, a superconducting material is grown by crystal growth on thesubstrate having the nano stripes formed thereon, by sputtering,vaporization, laser ablation, CVD, or MBE. Alternatively, the amorphousepitaxial process mentioned above may be used to form such asuperconducting thin film.

This process allows the superconducting material grown on the nanostripes to form amorphous or non-superconducting columnar defects andthe superconducting materials grown on those areas on the substrateother than where the nano stripes have been formed to form a thin filmof superconductor.

Mention is next made of a specific example of the superconducting thinfilm having pinning centers formed from nano dots.

Ag is used to make up nano dots. Using a RF (radio-frequency) sputteringapparatus, Ag nano dots are deposited on a single crystal substrate ofSrTiO₃ held at a temperature of 50° C., by sputtering from a Ag targetat a sputtering power of 10 W, with an Ar gas pressure of 6.3 Torr, andin a sputtering time period of 3 to 5 seconds. The sputtering apparatusis an off-axis sputtering apparatus in which the target plane is placedorthogonal to the substrate surface.

FIG. 3 is a view showing an image taken by an AFM (atomic forceMicroscope) of the Ag nano dots formed on the SrTiO₃ single crystalsubstrate. As is apparent from this view, it is seen that the Ag nanodots have diameters of 10 to 20 nm and heights not more than 5 to 6 nmand, being spaced apart from one another by an average distance of 50nm, are irregularly or randomly distributed. These dimensions andaverage distances are far much smaller than those of the nano dotsprepared by photolithography in the prior art. It should also be notedthat the size and surface density of nano dots are strongly dependent onthe deposition time and the substrate temperature.

Next, a superconducting thin film is grown on the substrate having thenano dots formed thereon. For its growth, use is made of APE (amorphousphase epitaxy). The process of growth of a superconducting thin film byAPE is shown below.

Using the RF sputtering apparatus, an amorphous film as a superconductorprecursor is deposited on the substrate having the Ag nano dots formedthereon, by sputtering from a sputtering target having a metalliccomposition of TlBaSrCa₂Cu₄ in a sputtering atmosphere with an Arpressure of 25 mTorr and an O₂ pressure of 5 mTorr by sputtering power100 W for 120 min., to a film thickness of 530 nm. To obtain acomparative specimen, such an amorphous film is also deposited on aSrTiO₃ single crystal substrate which has no Ag nano dots.

Next, the substrate and the comparative specimen substrate each havingthe superconductor precursor amorphous film formed thereon are enclosedin a sealed vessel made of Ag and subjected to a crystal growth processin a suitable Tl and O₂ atmosphere at a temperature of 845° C. and in atime period of 60 minutes, each to form a superconducting thin filmthereon.

Upon X-ray diffraction measurement, this superconducting thin film wasfound to be a (Cu, Tl)Ba₂SrCa₂Cu₃O_(y) superconductor.

The critical temperature was 104 K for both the superconducting thinfilm with the Ag nano dots and the superconducting thin film of thecomparative specimen without the Ag nano dots.

The dependency of the critical current density on the magnetic field ofeach of the superconducting thin film with the Ag nano dots and of thesuperconducting thin film without the Ag nano dots was measured. Theresults are shown in the graph of FIG. 4. The measurement was made by anAC susceptibility measurement, by using PPMS Model 6000, manufactured byQuantum Design Company. In the graph, the abscissa axis indicates theintensity of the magnetic field applied and the ordinate axis indicatesthe critical current density. The measurement temperature was 77.8 K.

As is apparent from the graph, it is seen that the superconducting thinfilm with the Ag nano dots is more than ten times higher in criticalcurrent density (Jc) than the superconducting thin film without the Agnano dots over an applied magnetic field intensity of 1. T.

It will also be apparent that the present invention is applicable to aselective reduction high temperature superconductor which is a Cu oxidehigh temperature superconductor, possible of positive hole doping byselective reduction of the constituent element as disclosed in PCTApplication No. PCT/JP00/01669, and is a (Cu, M) high temperaturesuperconducting material that can be expressed by the followingcomposition formula:Cu_(1−x)M_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)where M represents one or more metallic elements in an ionic form, theelements being selected from the group which consists of Tl, Bi, Pb, Hg,In, Ga, Sn, Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os, and Lrepresents one or more elements selected from the group which consistsof Mg and alkali metal elements, and where 0≦x≦1.0, 0=y≦1.0, 0≦z≦1,0≦w≦4, and 1≦n≦16.

INDUSTRIAL APPLICABILITY

The present invention thus provides an improved superconducting thinfilm which regardless of its type is at least ten times higher incritical current density than an exiting superconducting thin film andalso provides a method of manufacture whereby the improvedsuperconductor can be made quite inexpensively. Therefore, asuperconducting thin film thus obtained is extremely useful as appliedto the technical fields of cryogenic electronics and microwaves.

1. A superconducting thin film structure having columnar pinning centersand comprising: a substrate, nano dots or nano stripes which are formedinsularly on the substrate and three-dimensionally in shape and composedof a material other than a superconducting material and also other thana material of which the substrate is formed, amorphous ornon-superconducting columnar defects composed of a superconductingmaterial and grown on said nano dots or nano stripes, respectively, anda superconducting thin film composed of said superconducting materialformed in those areas on said substrate which are other than those wheresaid columnar defects are formed.
 2. A superconducting thin filmstructure having columnar pinning centers and comprising: a substrate,nano dots or nano stripes which are formed insularly on the substrateand three-dimensionally in shape and composed of a material other than asuperconducting material and also other than a material of which thesubstrate is formed, amorphous or non-superconducting columnar defectscomposed of a superconducting material and grown on said nano dots ornano stripes, respectively, a lattice defect which is formed on saidamorphous or non-superconducting columnar defects, and a superconductingthin film composed of said superconducting material formed in thoseareas on said substrate which are other than those where said columnardefects are formed.
 3. A superconducting thin film structure havingcolumnar pinning centers as set forth in claim 1 or claim 2,characterized in that said material other than a superconductingmaterial and also other than a material of which the substrate is formedis a metal, an insulator, a semiconductor or a ferromagnetic material.4. A superconducting thin film structure having columnar pinning centersas set forth in claim 1 or claim 2, characterized in that said nano dotsare 20 nm or less in diameter and approximately 6 nm in height, arespaced apart from one another by an average distance of 50 nm or less,and are irregularly or randomly distributed on said substrate.
 5. Asuperconducting thin film structure having columnar pinning centers asset forth in claim 1 or claim 2, characterized in that said nano stripesare formed, each in the form of a stripe, along flanks of steps formedon said substrate, and said substrate is formed so that its facialorientation is inclined to its crystallographic axis.
 6. Asuperconducting thin film structure having columnar pinning centers asset forth in claim 1 or claim 2, characterized in that said amorphous ornon-superconducting columnar defects are formed columnarly perpendicularto a surface of said substrate.
 7. A superconducting thin film structurehaving columnar pinning centers as set forth in claim 2, characterizedin that said lattice defect comprises a crystal dislocation of a portionof said superconducting thin film.
 8. A method of making asuperconducting thin film structure having columnar pinning centerscomprising the steps of forming insularly on a substrate, nano dots ornano stripes shaped three-dimensionally and composed of a material otherthan a superconducting material, and also other than a material of whichthe substrate is formed, and growing on said substrate and on said nanodots or nano stripes, a superconducting thin film composed of saidsuperconducting material, to form amorphous or non-superconductingcolumnar defects on said nano dots or nano stripes and to formsuperconducting thin film on those areas on the substrate other thanwhere said nano dots or nano stripes have been formed; wherein saidsuperconducting thin film structure comprises said substrate, nano dotsor nano stripes which are formed insularly on the substrate andthree-dimensionally in shape and composed of a material other than asuperconducting material and also other than a material of which thesubstrate is formed, amorphous or non-superconducting columnar defectscomposed of said superconducting material and grown on said nano dots ornano stripes, and a superconducting thin film composed of saidsuperconducting material formed in those areas on said substrate whichare other than those where said columnar defects are formed.
 9. A methodof making a superconducting thin film structure having columnar pinningcenters as set forth in claim 8, characterized in that saidthree-dimensionally shaped nano dots composed of a material other thansaid superconducting material are formed by depositing said materialinsularly on said substrate by a technique selected from the group whichconsists of sputtering, vaporization, laser ablation, CVD and MBE whilecontrolling the substrate temperature, the deposition rate of saidmaterial and the film thickness of said material deposited, therebycoagulating the deposited material on said substrate to form saidthree-dimensionally shaped nano dots insularly thereon.
 10. A method ofmaking a superconducting thin film structure having columnar pinningcenters as set forth in claim 8, characterized in that saidthree-dimensionally shaped nano stripes composed of a material otherthan said superconducting material, and also other than a material ofwhich the substrate is formed, are formed by forming a substrate so thatits facial orientation is inclined to its crystallographic axis, anddepositing said material insularly on said substrate by a techniqueselected from the group which consists of sputtering, vaporization,laser ablation, CVD and MBE while controlling the substrate temperature,the deposition rate of said material and the film thickness of saidmaterial deposited, thereby permitting the deposited material on saidsubstrate to selectively grow in regions of steps formed thereon andthereby to form said three-dimensionally shaped nano stripes insularlyon said substrate.
 11. A method of making a superconducting thin filmstructure having columnar pinning centers as set forth in claim 8,characterized in that said thin film of the superconducting material isgrown on said substrate by crystal growth of said superconductingmaterial, by way of sputtering, vaporization, laser ablation, CVD orMBE, on said substrate having said nano dots or nano stripes formedthereon.
 12. A method of making a thin film structure having columnarpinning centers as set forth in claim 8, characterized in that said thinfilm of the superconducting material is grown on said substrate bycrystal growth of said superconducting material, by way of amorphousphase epitaxial process, on said substrate having said nano dots or nanostripes formed thereon.